I read that there was not enough copper available to Europeans to get the bronze age going except for the huge ammounts that were mined in the Great Lakes area and that ancient smelted copper can be traced to its origins by studuying the impurities. Most of the bronze so studied is identical with copper in those Great Lakes mine areas which were mined throughout the bronze age and ceased to be used about the time iron supplanted bronze. The identity of the origins of the impurities was sloughed off by mainstream (the old guys in the universities) archaeologists as an obvious anomaly that just hasn’t been explained yet.
The problem I have with different takes on the idea that the Great Lakes copper fueled the Mediterranean bronze age (most recently, Gavin Menzies in his book on the Minoans) are the navigational barriers, such as Niagara Falls. Until the construction of the 18th- and 19th-century canals (to some extent), the Soo Locks, and the 20th century St Lawrence seaway, moving literally millions of tons of copper out of Lake Superior and into world trade routes, by water, appears to have been (ahem) impractical.
If it can found that there was an ancient PreColumbian canal system leading from Huron to Ontario for example, I’d probably be all on board, despite the major drop from Superior to Huron.
Another thing I’d regard as hard evidence would be an ancient, Med-style wreck (or ancient American wreck) loaded with copper and just setting where it sank, at the bottom of Lakes Superior, Huron, Erie, or Ontario, or as Menzies would have it, Lake Michigan.